MEASUREMENT OF LOW GLUCOSE-CONCENTRATIONS USING A MICROELECTROCHEMICAL ENZYME TRANSISTOR

Using poly(aniline), with glucose oxidase immobilised in an electroche mically polymerised film of 1,2-diaminobenzene deposited on top and us ing tetrathiafulvalenium as a mediator, microelectrochemical enzyme tr ansistors responsive to glucose which operate at pH 5 mere prepared. B y careful control and monitoring of both the initial electrochemical d eposition of the poly(aniline) and of the immobilisation of the enzyme , it was possible to achieve good reproducibility from device to devic e. By optimisation of the washing and resetting conditions, it was pos sible to achieve excellent reproducibilty for replicate measurements w ith a single device, Studies of the effect of the drain voltage on the device performance show that for drain voltages up to 0.35 V the mech anism of operation is unchanged and both the maximum drain current and the maximum switching rate at a given glucose concentration increase linearly with the drain voltage, Above 0.35 V, the performance of the device is degraded by other electrochemical reactions occurring on the poly(aniline). Measurements with low concentrations of glucose show t hat glucose concentrations in the micromolar region can be determined and that at the lowest levels the detection limit is determined by the background switching rate of the device in glucose-free buffer, For t he present devices the detection limit was found to be around 40 times lower than the detection limit for the same device operated as an amp erometric sensor in air-saturated buffer solution.